Ford F-650 2001 Owner's Manual page 173

Maintenance and care
• Battery tray with cover removed.
Motorcraft maintenance-free batteries do not normally require adding
additional water. However, for severe usage or in high temperature
climates, check the battery electrolyte levels. Refer to the Scheduled
Maintenance Guide for the service interval schedules.
Keep the electrolyte level in each cell up to the "level indicator".
Do not overfill the battery cells.
If the electrolyte level in the battery is low, you can add plain tap water
to the battery, as long as you do not use hard water (water with a high
mineral or alkali content). If possible, however, try to only fill the battery
cells with distilled water. If the battery needs water often, have the
charging system checked.
Make sure the battery cover/shield is reinstalled after the battery
has been cleaned or replaced.
For longer, trouble-free operation, keep the top of the batteries clean
and dry. Also, make certain the battery cables are always tightly fastened
to the battery terminals.
If you see any corrosion on the battery or terminals, remove the cables
from the terminals and clean with a wire brush. You can neutralize the
acid with a solution of baking soda and water.
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